My hair is black and I have the same natural highlights. I believe its caused by the products I use and it interacting with the sunlight causing my hair to lighten up. It was really crazy back in highschool....back then I was using products that contained alcohol(I didnt know any better) and during the summer my hair would show honey blond streaks. It was pretty nice and ever since then I've been wondering how I could duplicate that same look 20 years later.